Stereophonic sound, most commonly known as stereo sound, creates the illusion of a multidirectional audio perspective, with distinct audio sources coming from separate directions – as in natural hearing. The outcome is a more immersive and enjoyable audible experience.
Stereo speakers and stereo headphones work by reproducing sound from independent audio channels from the left and right sides. This contrasts with monophonic (or simply mono) sound, in which the same audio is played from all speakers as if coming from the same position.
Stereo speakers rely upon the availability of stereo audio recording to reproduce what some refer to as "true stereo." A stereo audio recording comprises two or more independent audio channels, which can be played independently through stereo speakers.
Although stereo systems provide a more true-to-life audio experience in comparison to mono systems, it's crucial to distinguish stereo from surround sound. The latter requires a specific recording process and a setup of at least five speakers strategically positioned to, as the name says, surround the listener.
Despite being scarce until recently, the availability of smartphones with stereo speakers is increasing. With this recent rise in mind, it's surprising to realize that the first smartphones with stereo speakers date quite a while back: the first ones might have been the Motorola 398 and E680 (both released in 2004), followed by the bulky LG VX-9800, a 2005 clamshell phone (also known as LG The V). The mobile market has clearly taken quite a while to warm up to stereo speakers.